[Info-vax] VMS - The new file system. What do we know about it?...

[Dirk Munk]

Paul Sture wrote:
> On 2016-11-15, Dirk Munk <munk at home.nl> wrote:
>> Paul Sture wrote:
>>> On 2016-11-14, Michael Moroney <moroney at world.std.spaamtrap.com> wrote:
>>>> Dirk Munk <munk at home.nl> writes:
>>>>
>>>>> Modern disks of course use the Advanced Format structure, with 4kB
>>>>> blocks/sectors. Using arbitrary 512 byte blocks is possible, but not
>>>>> very good for performance. Is that taken into consideration?
>>>>
>>>> That will have to be a separate project.  From what someone here told me
>>>> other OS's (Linux, Windoze) still use 4K block drives in 512 byte block
>>>> emulation mode.  Can anyone verify/refute this?
>>>
>>> If you look at the WD Red series of disks you will find that the 1TB,
>>> 2TB and 3TB models are 4K block capable but lie to the OS when asked
>>> if they support that.  Reading between the lines, this was to support
>>> the large numbers of Windows Server 2003 & XP systems still in use
>>> when this series of disks was released.
>>>
>>> There are O/S specific ways of overriding this, and with an OS which
>>> supports 4K disks, the main hurdle can be getting the disk formatted
>>> with 4K blocks.  Once formatted correctly, 4K will be used.
>>
>> I'm not quite sure what you mean. An OS always uses logical blocks when
>> formatting a disk, so does VMS. If you're using disk with 4kB sectors,
>> you have to make sure your logical blocks are a multiple of 4kB, and the
>> partitions always start at a sector boundary.
>
> Please see
>
> <http://wiki.illumos.org/display/illumos/ZFS+and+Advanced+Format+disks>
>
> In Paragraph 2:
>
>     If the disk reports that the physical sector size is 512 bytes, then
>     ZFS will use an internal sector size of 512 bytes. The problem is
>     that some HDDs misrepresent 4KB sector disks as having a physical
>     sector size of 512 bytes. The proper response should be that the
>     logical sector size is 512 bytes and the physical sector size is
>     4KB.  ...  In some cases, the HDD vendors advertise the disks as
>     "emulating 512 byte sectors" or "512e", ...
>
> Also see the summary in para 5.
>
> And using the command at the bottom of the page on my system, I get
> this>
>
>     zdb | egrep 'ashift| name'
>     name: 'backup'
>             ashift: 9
>     name: 'zones'
>             ashift: 12
>
> Where 'zones' is a mirrored pair of WD Red 3TB disks, and 'backup'
> is a mirrored pair of 1TB external USB disks bought in 2010.
>
>> Modern disk partitioning tools will always make sure partitions start at
>> a multiple of 1MB, which of course is also a multiple of 4kB.
>
> Can you give some examples of 'Modern disk partitioning tools'?

Sure, Gparted (or parted) is a good tool.

>
> One thing I noticed when XP was still around was that the Linux
> partitioning tools didn't set up disks entirely correctly for Windows.
> One clue may be the comment about the "XP Jumper" to offset LBA
> addresses by 1" mentioned in the above article.

That has nothing to do with XP. It is the way MBR partitioning works. 
The very first HDDs had tracks with a size of 63 blocks, so the first 
track was reserved for the partition table. Partition was done based on 
cylinder-head-sector values. These days partitions are based on block 
numbers, and I always start the first partition on block 2048 (1MB), and 
every partition has a size of multiple MBs.

Fdisk in Linux used the same MBR partitioning.

> Dunno, but there are
> still a lot of the smaller capacity disks out there whose design dates
> back to 2010 or before, particularly at the consumer level.
>
>